Magnetic memories, particularly magnetic random access memories (MRAMs), have drawn increasing interest due to their potential for high read/write speed, excellent endurance, non-volatility and low power consumption during operation. An MRAM can store information utilizing magnetic materials as an information recording medium. One type of MRAM is a spin transfer torque random access memory (STT-MRAM). STT-MRAM utilizes magnetic junctions written at least in part by a current driven through the magnetic junction. A spin polarized current driven through the magnetic junction exerts a spin torque on the magnetic moments in the magnetic junction. As a result, layer(s) having magnetic moments that are responsive to the spin torque may be switched to a desired state.
For example, FIG. 1 depicts a conventional dual magnetic tunneling junction (MTJ) 10 as it may be used in a conventional STT-MRAM. The conventional MTJ 10 typically resides on a substrate 12. A bottom contact 14 and top contact 24 may be used to drive current through the conventional dual MTJ 10 in a current-perpendicular-to-plane (CPP) direction, or along the z-axis as shown in FIG. 1. The conventional MTJ, uses conventional seed layer(s) (not shown), may include capping layers (not shown) and may include a conventional antiferromagnetic (AFM) layer (not shown). The conventional magnetic junction 10 includes a conventional bottom pinned layer 16, a conventional tunneling barrier layer 18, a conventional free layer 20, a conventional second tunneling barrier layer 22 and a conventional top pinned layer 30.
The conventional pinned layers 16 and 30 and the conventional free layer 20 and the conventional pinned structure 10 are magnetic. The magnetizations 17 and 31 of the conventional pinned layers 16 and 30, respectively, are fixed, or pinned, in a particular direction. Although depicted as a simple (single) layer, the conventional pinned layer 16 and/or 30 may include multiple layers. For example, the conventional pinned layer 16 and/or 30 may be a synthetic antiferromagnetic (SAF) structure including magnetic layers antiferromagnetically coupled through thin conductive layers, such as Ru. The conventional free layer 20 has a changeable magnetization 21. Although depicted as a simple layer, the conventional free layer 20 may also include multiple layers. For example, the conventional free layer 20 may be a synthetic layer including magnetic layers antiferromagnetically or ferromagnetically coupled through thin conductive layers, such as Ru.
To switch the magnetization 21 of the conventional free layer 20, a current is driven perpendicular to plane (in the z-direction). When a sufficient current is driven from the top contact 22 to the bottom contact 14, the magnetization 21 of the conventional free layer 20 may switch to be parallel to the magnetization 17 of the conventional pinned layer 16. When a sufficient current is driven from the bottom contact 11 to the top contact 22, the magnetization 21 of the free layer may switch to be antiparallel to that of the pinned layer 16. The differences in magnetic configurations correspond to different magnetoresistances and thus different logical states (e.g. a logical “0” and a logical “1”) of the conventional MTJ 10.
Because of their potential for use in a variety of applications, research in magnetic memories is ongoing. Mechanisms for improving the performance of STT-RAM are desired. For example, a high perpendicular magnetic anisotropy and a high magnetoresistance are desired. Accordingly, what is needed is a method and system that may improve the performance of the spin transfer torque based memories. The method and system described herein address such a need.